1. Field of the Invention
The present invention relates to a camera using a recording medium in which an object image obtained through a photographing optical system is electronically developed, and more particularly, to a device for determining an electric voltage applied to the recording medium.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Unexamined Patent Publication No. 5-2280 and U.S. Pat. No. 5,424,156, there is known a photographic material which is directly electronically developed so that the developed visible image can be immediately obtained. In this specification, such a recording medium is referred to as an electro-developing recording medium, and an electronic still camera using the electro-developing recording medium is referred to as an electro-developing type camera.
Japanese Unexamined Patent Publication Nos. 5-165005, 6-130347 and 7-13132 disclose an electro-developing recording medium which comprises a liquid crystal display having a memory-type liquid crystal so that an image indicated on the liquid crystal display is kept, even if the electric field applied to the liquid crystal display is removed. '347 and '132 disclose an electro-developing recording medium in which the electrostatic information recording medium and the electric charge storage medium are combined to form one body. Namely, in these electro-developing recording mediums, even if an electric voltage applied thereto is removed, the image formed on the electro-developing recording medium is kept.
For recording a clear image on the electro-developing recording medium, the applied electric voltage and the voltage application period on the recording medium are important components (see Japanese Unexamined Patent Publication No. 6-313872). These components depend upon the characteristics, i.e., the resistances and the electrostatic capacities of an electric charge storage medium and an electrostatic information recording medium which are provided in the electro-developing recording medium. Especially, the resistance of the electrostatic information recording medium is greatly affected by the environment such as temperature around the electro-developing recording medium. Namely, by detecting the resistance before the recording operation, the applied electric voltage and the voltage application period on the electro-developing recording medium can be properly controlled.
For detecting the resistance of the electrostatic information recording medium, it is necessary that an electric voltage is applied thereto while the electrostatic information recording medium is shut from ambient daylight, and a dark current, i.e., an electric current flowing therein is sensed. However, since the electrostatic information recording medium has an electrostatic capacitance due to the structure thereof, and is equivalent to an electric circuit in which a resistor and a capacitance are connected in parallel, a relatively long time is needed before the electric condition of the electrostatic information recording medium becomes stable so that the dark current can be sensed.